i

DESIGN SUBSTRATE INTEGRATED WAVEGUIDE SLOT ARRAY

ANTENNA AT X-BAND

By

ESRA’A MOUSA ABDEL RAHMAN ALI

FOR PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR MASTER DEGREE ELECTRONIC SYSTEMS DESIGN

ENGINERRING.

JUNE 2013

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ACKNOWLEDGMENT

In the name of Allah, Most Gracious, Most Merciful.

I would like to thank my supervisor Dr. Aftanasar whose insightful guidance and

helpful and open demeanor allowed me to complete this thesis. I am thankful to my

family members, especially to my father and mother. Their prayers provided me a

constant source of inspiration. I wish to dedicate this thesis to my beloved husband Bilal

Alqasem; my children Hasan and my new baby Taleen. I am greatly indebted to their

enthusiasm and strong support. Finally, thanks to all who have provided helpful

suggestions and encouragements.

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TABLE OF CONTENTS

TABLE OF CONTENTS ........................................................................................... iii

LIST OF TABLES...................................................................................................... vi

LIST OF FIGURES ................................................................................................... vii

LIST OF SYMBOLS .................................................................................................. xi

LIST OF ABBREVIATIONS ................................................................................... xii

ABSTRAK ................................................................................................................ xiii

ABSTRACT ............................................................................................................... xv

CHAPTER 1 ................................................................................................................ 1

1.1 Overviow ........................................................................................................... 1

1.2 Problem statement.............................................................................................. 2

1.3 Thesis aims and objectives ................................................................................. 3

1.4 Scope of research ............................................................................................... 3

1.5 Motivation and applications ............................................................................... 4

1.6 Thesis outline..................................................................................................... 5

CHAPTER 2 ................................................................................................................ 8

2.1 Introduction ....................................................................................................... 8

2.2 Substrate Integrated Waveguide (SIW) ............................................................ 10

2.3 Longitudinal slots ............................................................................................ 15

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2.4 Waveguide slot radiator ................................................................................... 18

2.5 Theory of transition microstrip line to Substrate Integrated Wave guide ........... 22

2.6 Theoretical calculations ................................................................................... 26

2.6.1 Equivalent rectangular waveguide using SIW ......................................... 26

2.6.2 Design technique for microstrip transition .............................................. 29

2.6.3 Design Technique for slots ..................................................................... 32

2.7 Summary ......................................................................................................... 34

CHAPTER 3 .............................................................................................................. 35

3.1 Introduction ..................................................................................................... 35

3.2 Flow chart for design process ........................................................................... 35

3.3 Numerical results for SIW................................................................................ 37

3.4 Transformation from SIW to microstrip ........................................................... 38

3.5 Simulation ....................................................................................................... 42

3.5.1 CST studio suite ..................................................................................... 43

3.5.2 CST Microwave studio ........................................................................... 44

3.5.3 Design steps ........................................................................................... 44

CHAPTER 4 .............................................................................................................. 53

4.1 Introduction ..................................................................................................... 53

4.2 Steps of simulation SIW slot antenna ............................................................... 53

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4.2.1 Designing the SIW slot antenna with 1 port before adding the microstrip line 54

4.2.2 Design SIW slot antenna with 1 port after adding the microstrip line ...... 57

4.3 Comparison between SIW slot antenna before and after adding the microstrip line

61

CHAPTER 5 .............................................................................................................. 63

5.1 Conclusion ....................................................................................................... 63

5.2 Future work ..................................................................................................... 64

REFERENCES ............................................................................................................... 65

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LIST OF TABLES

Table 1.1: Comparison between the methods……………………………………..34

Table 3.1: Dimensions of Substrate Integrated Waveguide………………………38

Table 3.2: Dimensions of microstrip…………………………….………..……….39

Table 3.3: values of the slots …………………………………………..…………40

Table 4.4: comparison of Microstrip on SIW slot antenna …..…………………62

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LIST OF FIGURES

Figure 1.1: Picture of a slotted waveguide antenna ……………….……………….4

Figure 2.1: Substrate integrated waveguide and the equivalent rectangular waveguide ……………………………………………….………….10

Figure 2.2: a) Sketch of a SIW. b) Periodic cell of SIW. c) Enclosed periodic cell.………………………………………………...…….…………..11

Figure 2.3: Diagram of via holes with the surface impedance concept.……..…….14

Figure 2.4: Front and rear view of the slotted SIW array antenna………..……….17

Figure 2.5: Slotted SIW array antenna fed by a microstrip line…..…….……..…..18

Figure 2.6: waveguide slot antenna ……………………….………………………19

Figure 2.7: Slots cut in the walls of a rectangular waveguide…………..…………20

Figure 2.8: Linear resonant waveguide slot arrays with longitudinal slot elements. ………………………………………………………………………22

Figure 2.9: Transition between microstrip line and dielectric-filled waveguide ……………………………………………………………………….23

Figure 2.10: Transition between a microstrip line and a SIW……….……….…….23

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Figure 2.11: Back-to-back transition between a microstripline to SIW…….……..24

Figure 2.12: Transition between a grounded coplanar waveguide and a SIW with the use of a current probe……………………..…………………….. 25

Figure 2.13: (a) SIW and the equivalent rectangular waveguide (b) top view of an

SIW……..........................................................................................................................26

Figure 2.14: Configuration of the microstrip-to-SIW transition………………………..27

Figure 2.15: Equivalent topology for the microstrip-to-SIW transition………………..31

Figure 2.16: Microstrip to Waveguide Transition…………………………….………..32

Figure 3.1: Flow chart of the process design……………………………………….….36

Figure 3.2: line calculation tool to calculate the values of W, L for microstrip line . ………………………………………………………………………39

Figure 3.3: Designing of microstrip line using ADS ………………………………40

Figure 3.4: designing of rectangular waveguide using ADS ……………………..41

Figure 3.5: Return loss of rectangular waveguide……………….…………………41

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Figure 3.6: Screenshot of CST microwave studio…………..……………………... 44

Figure 3.7: Working plane properties............................................................................39

Figure 3.8: The unit box.................................................................................................39

Figure 3.9: Design the substrate....................................................................................40

Figure 3.10: Design the top face of the antenna………………………………………..41

Figure 3.11: Design the bottom face (ground) of the antenna…………………………41

Figure 3.12: Design the vias…………………………………………………………..42

Figure 3.13: Transform the vias.………………………………………………………43

Figure 3.14: Design the slots…………………………………………………………43

Figure 3.15: The final design of the antenna…………………………………………44

Figure 3.16: Set the frequency …………………………………………………........44

Figure 3.17: Set the boundary conditions……………………………………………45

Figure 3.18: Set the waveguide port………………………………………………….45

Figure 3.19: Choose the fields monitor………………………………………………52

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Figure 4.1: SIW slot antenna before adding the microstrip …………………...….54

Figure 4.2: Return loss of the SIW five-slots array antenna before adding the microstrip……………………………..……………………………..55

Figure 4.3: Simulated E-plane radiation at a frequency of 10.5 GH…..……………56

Figure 4.4: Simulated H-plane radiation at a frequency of 10.5 GHz..….…………57

Figure 4.5: SIW slot array antenna. a = 13.28 mm, equ a = 13.14 mm, d = 0.5 mm, s = 2 mm, εr = 3.38 . Design frequency is 10GHz…………………. 58

Figure 4.6: Return loss of the SIW five-slots array antenn…..……………………59

Figure 4.7: Simulated E-plane radiation at a frequency of 10.47 GHz in polar form…………………………………………...………………………60

Figure 4.8: Simulated H-plane radiation at a frequency of 10.47 GHz in polar form………………………………………………………….. 61

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LIST OF SYMBOLS

Θ Theta, angle

휋 Pi

S Via hole spacing

D Via hole diameter

A Substrate integrated waveguide width

B Substrate integrated waveguide height

aRWG waveguide width

F Frequency

E electric field

H magnetic field

X Offset

Vs Slot voltage

Fc cutoff frequency

Co Speed of light

W Slot width

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LIST OF ABBREVIATIONS

RT Return loss

BW Bandwidth

Zo High impedence

ADS Advance design system

CST Computer Simulation Technology

RWG Rectangular Waveguide

BI-RME Boundary Integral-Resonant Mode Expansion

Λg Guide Wavelength

SIW Substrate Integrated Waveguide

TE Transverse Electric

SIW Substrate integrated waveguide

H Dielectric substrate

Εr Dielectric constant

dB Decibel

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REKA BENTUK SUBSTRATE PEMANDU GELOMBANG

BERSEPADU SLOT PENYIAR ANTENA PADA JALUR X

ABSTRAK

Pandu gelombang bersepadu Substrat (SIW) adalah pandu gelombang berisi

segiempat dielektrik, yang disintesis dalam satu satah substrat dengan tatasusunan laluan

logam yang mengambil kira dinding sebelah dua hala dan peralihan dengan struktur

satah. Laluan ini bertindak sebagai dinding pemandu gelombang yang menyokong aliran

semasa, sekali gus membolehkan pemanduan gelombang mod mencapah. Substrat

pemandu gelombang bersepadu dicadangkan untuk mengurangkan kehilangan gelombang

yang minima, kos dan sesuai untuk aplikasi bersepadu yang bekepadatan tinggi. SIW

mengekalkan kelebihan dari kedua-dua hala gelombang tradisional segi empat tepat dan

mikrostrip untuk integrasi yang mudah. Ia digunakan dalam mereka bentuk litar pasif

seperti resonator, Pengganding, penapis, pembahagi kuasa dan antenna

.

Dalam tesis ini, kami mengkaji gelombang SIW dan mencadangkan SIW

sebagai slot antena pemandu gelombang antena. Slot pemandu gelombang antena direka

mengikut prosedur reka bentuk yang diubahsuai oleh Elliot. Prosedur reka bentuk

diubahsuai Elliot mengambil kira kesan-kesan gandingan bersama daripada slot penyiar

bersebelahan. Antena ini kemudiannya ditukar kepada substrat antena bersepadu slot

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pemandu gelombang dengan cermat dan meletakkan dua baris logam melalui lubang

untuk mensimulasi dinding sisi dari pandu gelombang segi empat tepat. Saiz dan lokasi

melalui lubang dikira seperti yang terkandung pada medan elektromagnet dalam substrat

pemandu gelombang bersepadu dengan mengabaikan kehilangan dan substrat pemandu

gelombang bersepadu mempunyai ciri impedance dan penyebaran berterusan yang sama

seperti pemandu gelombang segi empat . .

Antena tersebut disokong kepada garisa; garis mikrostrip adalah salah satu jenis

yang paling popular dalam talian penghantaran satah terutamanya kerana ia boleh direka

oleh proses fotolitografi yang mudah, bersaiz kecil dan bersepadu dengan kedua-dua

peranti mikro pasif dan aktif. .

SIW direka dalam band-X, dengan radiasi yang baik pada sidelobes -51.78 dB di

bawah rasuk utama diperhatikan. Antena ini mempunyai jalur lebar impedans 280 MHz

pada frekuensi operasi 10 GHz.

xv

DESIGN SUBSTRATE INTEGRATED WAVEGUIDE SLOT ARRAY

ANTENNA AT X-BAND

ABSTRACT

Substrate integrated waveguide (SIW) is a rectangular dielectric-filled waveguide,

which is synthesized in a planar substrate with arrays of metallic vias to realize bilateral

side walls and its transitions with planar structures. These vias act as walls of the

waveguide supporting current flow, thus allowing for waveguide mode propagation. SIW

is suggested for low-loss, low-cost and high density integration applications. SIW

preserves the advantages from both the traditional rectangular waveguide and microstrip

for easy integration. It is used in designing passive circuits such as resonators, couplers,

filters, power dividers, circulators, and antennas.

In this thesis substrate integrated waveguides were investigatedand their

application as a slotted waveguide antenna. The standard slotted waveguide antenna is

designed following Elliot's modified design procedure. Elliot's modified design procedure

takes into account the effects of mutual coupling from the neighboring slots in the array.

The antenna is then converted to a slotted SIW antenna by carefully placing two rows of

metallic via holes to simulate the sidewalls of the rectangular waveguide. The size and

location of the via holes are calculated such that they contain the electromagnetic fields

xvi

inside the SIW with negligible leakage loss and that the SIW has the same propagation

constant and characteristic impedance as its equivalent rectangular waveguide.

The antenna is fed by a microstrip line, microstrip line is one of the most popular

types of planar transmission lines primarily because it can be fabricated by

photolithographic processes and is easily miniaturized and integrated with both passive

and active microwave devices.

The SIWis designed on X-band, a good radiation pattern with sidelobes -51.78 dB

below the main beam is observed. The antenna has an impedance bandwidth of 280 MHz

at the operating frequency of 10 GHz.

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CHAPTER 1

INTRODUCTION

1.1 Overview

The slotted waveguide antenna is a type of antenna. It can provide a great gain

and has high power handling abilities and finds a lot of applications. The physical

structure of a waveguide is large and it needs complicated transitions for connection

with planar circuitry. Rectangular waveguides and the transitions needed to integrate

them with planar circuitry are expensive and bulky. Substrate integrated waveguides

(SIWs) are a relatively new type of planar transmission line which essentially

integrate a waveguide into a planar circuit such as a printed circuit board or a low-

temperature co-fired ceramic. SIW incorporate the advantages of rectangular

waveguides, such as high power handling capacity, high Q-factor and low loss, into

planar circuitry(Deslandes and Wu, 2006). In addition SIWs allow for easy transition

between other planar transmission lines and they are small, have a low-profile and

weigh less compared to the rectangular waveguides (Deslandes and Wu, 2006).

SIW has the similar character of the rectangular waveguide (RWG), many

design concepts of conventional RWG could be transferred to this new platform, such

as the waveguide divider, filter, antenna, etc.(Yao and Zhiyuan, 2005).SIW is used for

radar and communication systems which require narrow- beam or shaped-beam.

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Rectangular waveguide can be used to design high Q components in wireless

systems but requires complex transitions to integrated planar circuits(Nam et al.,

2005).Integrating rectangular waveguide into microstrip substrate reduce Q- factor of

waveguide because of dielectric filling and volume reduction(Deslandes and Wu,

2001).

In this research, the conventional RWG slot array antennawas transferred to

the SIW slot array antenna, which is fed by a microstrip line. As a result, not only the

size, weight and cost of the waveguide slot array antenna are reduced, but also the

manufacturing repeatability and consistency are enhanced. But comparing them with

RWG slot array antenna, the gain and efficiency are lesser and the side lobe level is

higher because of the leakage.

1.2 Problem statement

Rectangular waveguide components have broadly been used in millimeter-

wave systems. Their relatively high cost and hard integration prevent them from being

used in low-cost high-volume applications. The recently proposed SIW scheme

provides an interesting alternative. In this case by transferring the conventional

waveguide resonant slot array antenna to the SIW structure, could get the advantages

of the resonant slot array antenna as well as the advantages of the SIW such as small

size, low profile, low cost.

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1.3 Thesis aims and objectives

The aim in this work is designing SIW five- slot array antenna at band 8-12

GHz using substrate integrate waveguide theory at resonance freqency of 10 GHz. In

order to fulfil the implementation of this research there are main objectives need to be

achieved:

1. To use the mathmatical equations to calcualte the physical parmeters of the

SIW slot array antenna.

2. Using the physical paramters of SIW slot array antenna to design it through

CST microwave studio.

3. To characteristic the SIW five slot array antenna.

1.4 Scope of research

SIW slot array antenna will be designed at band 8-12 GHz using RO4003

through CST microwave studio and show the return loss at resonance frequency of 10

GHz, after that discussing the effect of using microstrip feed line in feeding the slot

antenna. Finding the physical parameters of the SIW slot antenna will be calculate

using the equations in the theoretical part.

4

1.5 Motivation and applications

The slotted waveguide antenna is an aperture antenna. Big arrays can be

molded with this type of antenna. Figure 1.1 shows a picture of a slotted waveguide

antenna.

Figure 1.1: Picture of a slotted waveguide antenna (Gilbert, 2007).

This property lets designers to design slotted waveguide antennas with a large

amount of gain and similarly a very narrow beam width. A waveguide itself is very

durable and has a high power handling capacity. waveguide antenna used in many

applications. The slotted waveguide antenna is especially well fitted for radar

applications thanks to its large gain and small beam width.

5

Unfortunately waveguides are heavy objects. They cannot be easily integrated

with other microwave circuitry. Expensive transitions must be designed and built in

order to connect the waveguide to the rest of the microwave circuit (Xu and Wu,

2005). This work is concerned with taking a slotted waveguide antenna and

integrating it directly into the substrate.

This work also develops a feeding scheme that allows the integrated antenna

to be fed through a basic microwave transmission line, the microstrip. There are some

definite advantages to integrating a slotted waveguide antenna directly into the

substrate. First of all, the transitions between a waveguide and a planar circuit are no

longer needed. These transitions must be carefully built and are very difficult to mass

produce.Having the waveguide integrated into the substrate allows the overall circuit

to have a smooth low profile appearance.

1.6 Thesis outline

The organization of this report is as follow:

Chapter 1

Chapter 1 consists of the introduction part of the project such as the

background, problem statement, objectives of the project, the scopes of the project

and Motivation & Applications.

6

Chapter 2

Chapter Two focuses on literature review. It is mainly explain the concept of the

project in details. It is also include the review of several projects that have been made

by researchers from other university. With doing this, the results between these

projects with others can compare and the differences more clearly. Focusing on

previous work on the design of a slotted waveguide antenna and the improvements on

design procedure are discussed. Works on substrate integrated waveguides and how

their characteristics are extracted are presented. Work on slotted substrate integrated

waveguide antennas are mentioned with some results listed. Previous work

concerning transitions between microstrip lines and SIW are discussed in chapter 2.

Chapter 3

Chapter Three is a methodology. It is included with block diagram, the method

used to complete this project. And simulation of SIW slot antenna using CST

microwave. During this, it will review about the model.

Chapter 4

Chapter Four shows the results and discussions. It will cover all the result of

the analysis and designing the project and one of them is the progress of the project.

The design, simulation and results are presented and analyzed.

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Chapter 5

The conclusion will be discussed in Chapter Five. The conclusion has been

made and for the future works, there is also recommendation added. The

recommendation is added to give an opinion and also an improvement on how the

future works should have done.

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Previous research related to slotted waveguide antennas, substrate integrated

waveguides, substrate integrated waveguide antennas and transitions between

microwave transmission lines and substrate integrated waveguides are discussed in

this chapter.

Conventional waveguides, the first generation of microwave guiding structures

had the benefits of having high power carrying capacity and high Q-factor, but also

had the disadvantages of being big. The next generation of microwave guiding

elements was the strip-like or slot-like planar printed transmission lines used in

Microwave Integrated Circuits (MICs).These were planar low profile structures but

lacked the high power carrying capacity and high Q-factor of the conventional

waveguides. To link the gap between MIC structures and conventional waveguides,

Substrate Integrated Circuits (SICs) were developed which are planar low profile

structures like MIC structures, also having high power carrying capacity and high Q-

factor like waveguides(K.wu, 2003). Principle of operation of SIC was to build

artificial channels within the substrate to guide the waves. Two techniques are used to

build these channels (which are embedded in the substrate).One is to use metallic vias

which act as sidewalls. Other technique uses contrast in values of εr so that

9

phenomenon of total internal reflection can take place and the wave gets confined

within the artificial channel (Wu, 2010). A SIW is one of the topologies of SIC. The

SIW technology has been well applied to several microwave and millimeter-wave

components, including active circuits, passive components and antennas (Srivastava.,

2012 ).

The feasibility of the concept has been proven for microstrip transitions by

Deslandes, Wu, Jain and Kinayman. Coplanar waveguide transition has also been

designed by Deslandes and Wu and Ito and al. Simple waveguide filter has been

presented by Ito and al. and Tzuang and al. Furthermore, the radiation loss generated

from gaps between vias has been unknown (Samah, 2011.).

Integrating rectangular waveguide intomicrostrip substrate reduce Q-factor of

waveguide because of dielectric filling and volume reduction (Deslandes and Wu,

2001).

SIW is equivalent to a conventional rectangular wave guide filled with

dielectric, hence it can be analyzed just by using width of equivalent waveguide(Yan

et al., 2004). The width of equivalent RWG is calculated by an experiment formula,

Figure 2.1 shows the physical parameter required in the equivalent rectangular

waveguide

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Figure 2.1: Substrate integrated waveguide and the equivalent rectangular waveguide (Yan et al., 2004).

Recently, the concept of the integrated rectangular waveguide has been

proposed in which an artificial waveguide is synthesized and constructed with linear

arrays of metalized via-holes or posts embedded in the same substrate used for the

planar circuit. This waveguide can also be realized with complete metallized walls.

Several transitions have been proposed to excite the waveguide. In all these structures,

the planar circuits, such as a microstrip line or coplanar waveguide, and the

rectangular waveguide are built onto the same substrate and the transition is formed

with a simple matching geometry between both structures. Judging from its electrical

performance, the synthesized integrated waveguide is a good compromise between the

air-filled rectangular waveguide and planar circuit (Surarman, 2011).

2.2 Substrate Integrated Waveguide (SIW)

SIW is a new form of transmission line that has been promoted in the past few

years by some researchers. A large variety of components such as couplers, detectors,

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isolators, attenuators and slot lines, are commercially available for various standard

waveguide bands from 1 GHz to over 220GHz. Because of these trends towards

miniaturization and integration, most microwave circuitry is currently manufactured

using planar transmission lines such as microstrips transition, coplanar transition and

so on. At the same time, the waveguides needs many applications such as high power

systems, millimetre wave systems and some precision test systems.

Cassiviet analyzed substrate integrated waveguides (SIWs) using the BI-RME

method combined with Floquet's theorem to determine the dispersion characteristics

of the SIW (Cassivi et al., 2002). The SIW is composed of a substrate covered on the

top and bottom with a thin metallic sheet and metallic via holes are used to simulate

the side walls of a rectangular waveguide.

Figure 2.2: a) Sketch of a SIW. b) Periodic cell of SIW. c) Enclosed periodic cell.(Cassivi et al., 2002)

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The SIW is a periodic structure; figure 2.2 shows a picture of a SIW and of a

periodic cell of a SIW. A generalized admittance matrix of the periodic cell is

determined using the BI-RME method. Due to the periodic nature of the SIW,

Floquet's theorem can be used to obtain an eigenvalue system. The eigenvalues give

the propagation constants of the TE modes propagating through the SIW and the

eigenvectors give the pattern of the modal fields. Their works have shown that

substrate integrated waveguides have the same basic guided wave characteristics as

rectangular waveguides. They have derived empirical formulas which estimate the

cutoff frequencies of the first two dominant modes of the SIW.

And

Where (a) is the SIW width, (d) is the diameter of via holes, (s) is the spacing

between adjacent via holes and Co is the speed of light. By comparing equation (2.1)

with the equation that determines the cutoff frequency of the dominant mode of

rectangular waveguides, Cassivietalhave derived an equation that relates the width of

a SIW to an equivalent width of a rectangular waveguide(Cassivi et al., 2002).

13

SIW is a periodic structures which are much more complex to design when

compared to a conventional waveguide. Deslandes and Wu have developed a simple

design procedure which transforms an SIW into an equivalent rectangular waveguide

(Deslandes and Wu, 2006).Use available finite element software package. This allows

the designer to design a system using a conventional waveguide then follow their

procedure to find an equivalent SIW to replace the rectangular waveguide.

Deslandes and Wu have developed a method for determining the complex

propagation constant of a SIW using the concept of surface impedance to model the

rows of conducting cylinders which act as the sidewalls of a SIW (Deslandes and Wu,

2006). The proposed model is solved using a method of moments and a transverse

resonance procedure. An electromagnetic field of a TE mode wave propagating

through a waveguide can be represented by a superposition of two waves propagating

at an angle 0 to the z-axis, in this case the direction in which the energy is propagating

(Deslandes and Wu, 2006). At the cutoff frequency the TEM waves are scattered by

the two conducting rows of metallic via holes. Each row of via holes can be

represented by surface impedance ZS. Figure 2.3 shows a diagram of the two rows of

via holes.

14

Figure 2.3: Diagram of via holes with the surface impedance concept (Deslandes and

Wu, 2006).

A rectangular waveguide equivalent width (ae) of the SIW can be calculated

with a transverse resonance procedure. The propagation constant of the SIW can be

considered by the reflection coefficient of the row of via holes at the wanted cutoff

frequency. The reflection coefficient of the via holes at the cutoff frequency can be

calculated with a method of moments technique. The novelty of this method is that the

propagation constant of the SIW can be calculated both accurately and quickly. This

method can be further used to extract not only the guided-wave properties of the SIW

but also the leakage characteristics of the periodic structure. From these results design

rules have been suggested to follow in order to minimize leakage and avoid band gaps

in the operating bandwidth and to overall assist the designer design substrate

integrated waveguides. The first design rule is straight forward and states that the

separation distance (s) must be larger than the via hole diameter (d). The second

15

design rule states that the separation distance must be smaller than a quarter

wavelengths at the cutoff frequency. In order to confirm negligible leakage loss

between the metallic cylinders a third design rules states that the separation distance

should be smaller than 2d. Good experimental results were shown to validate the

theory described above.

2.3 Longitudinal slots

Yan et al. have designed a 4x4 SIW slot antenna array(Yan et al., 2005). The

whole antenna and feeding system are integrated in one substrate which leads to small

size, low profile and low cost. Longitudinal slots were etched on the top metallic

surface of a SIW making use of work done by Elliot. They determined the equivalent

width of a rectangular waveguide for a SIW through the following equations.

Where

16

The equivalent width of a rectangular waveguide in terms of the width of the

corresponding SIW is given by

Where a; is the width of the SIW. This method for determining the equivalent

width is precise to within 1%. This method is more accurate than the one described by

Cassivi et al. in equation (2.3). A picture of the antenna is given in figure 2.4. The

antenna is fed through a network of microstrip lines feeding each SIW. Results show a

l0 dB bandwidth of 600MHz centered at 10GHz, however the return loss at the center

frequency is found to be 1ldB.(Cassivi et al., 2002)

17

Figure 2.4: Front and rear view of the slotted SIW array antenna (Yan et al., 2005)

Weng et al. have designed a 5-slot SIW antenna array for the Ku-band.(Weng

et al., 2006) Longitudinal slots are etched on the top metallic surface of an SIW in a

manner similar to (Yan et al., 2005) The whole antenna is integrated on one substrate

for small size and easy manufacturability. A picture of the antenna they built is given

in figure 2.5 Results show a l0 dB bandwidth of 500MHz centered about 14.7GHz

with a center frequency return loss of 20dB.

18

Figure 2.5: Slotted SIW array antenna fed by a microstrip line(Weng et al., 2006).

2.4 Waveguide slot radiator

Slot antennas are common omnidirectional microwave antennas. These

antennas feature omnidirectional gain around the azimuth with horizontal

polarization. Waveguide slot antennas are often used as omnidirectional microwave

antennas. The slot array was invented in 1943 at McGill University in Montreal.

Unique features of these antennas are horizontal polarization and omnidirectional gain

around the azimuth. They are fairly easy to build. While they have been described in

several articles in the ham literature, all the articles seem to have the same

dimensions, suggesting a common genesis (Wade, 2001).

19

Figure 2.6: Waveguide slot antenna (Wade, 2001)

The radiating elements of a waveguide slot array are integral part of the feed

system. A familiarization with the modal fields within a waveguide is a necessary to

understand where to place slots. Narrow slots that are parallel to waveguide wall and

it interrupt the flow of current forcing it to go around the slots, figure 2.6 shows that.

Figure 2.7 shows the slots cut in the walls of a rectangular waveguide. Slot g

does not radiate because the slot is lined up with the direction of the sidewall current.

Slot h does not radiate because the transverse current is zero there. Slots a, b, c, i, and

j are shunt slots because they interrupt the transverse currents (Jx ,Jy) and can be

represented by two-terminal shunt admittances. Slots e, k, and d interrupt Jz and are

represented by series impedance. Slot d interrupts Jx, but the excitation polarity is

20

opposite on either side of the waveguide centre line, thus preventing radiation from

that current component. Both Jx and Jz excite slot f. A Pi- or T-impedance network

can represent it. (Gilbert, 2007)

Figure 2.7: Slots cut in the walls of a rectangular waveguide. (Gilbert, 2007)

Slotted waveguide array designs, it contains a numerous stick arrays placed

side by side; the mutual coupling between slots is high, it is used for radiating

aperture and for feeding network that made from waveguide.

The distance between short circuit wave guide termination and first end slot is

g /4. The short circuit reflects as an open circuit, which has an admittance of zero, to

the first slot from the end. This is in parallel with the conductance of the end slot.

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Linear slotted arrays operate either longitudinal shunt slots or edge-wall shunt

slots as radiating elements. Narrow longitudinal shunt slots radiate array patterns that

have very high cross-polarization isolation. An example of an end-fed, dual-sided

longitudinal linear slot array is an X-band array, as shown in Figure 2.8. For this

array, slots have been placed on both wide walls of the waveguide. The array radiates

an omni-azimuthal, horizontally polarized pattern. For a vertically polarized pattern,

the array would have to be involved of edge-wall shunt slots, which are also excited

by a single transverse current. However, the cross-polarization isolation with edge

slots is not as good as with the longitudinal slots because every other element is

canted in a different direction, and the polarization clarity is dependent on the uniform

excitation of the slots and external cancellation of the cross-polarized field

components. Rotated series slots also have a lower cross-polarization isolation level

as compared with the longitudinal shunt slots and edge slots due to the rotation of the

slots and due to some excitation of the slots by the transverse currents.

Slot elements are located on both sides at waveguide to provide an omni-azimuthally

(Gilbert, 2007).

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Figure 2.8: Linear resonant waveguide slot arrays with longitudinal slot ele-ments. In (a) the array is fed from the waveguide end. In (b) the

array is fed from the center through an E-plane T coupler (Gilbert, 2007).

2.5 Theory of transition microstrip line to Substrate Integrated Wave guide

Deslandes and Wu Have presented a transition between a microstrip line and

planar dielectric-filled waveguide fabricated on the same substrate (Deslandes and

Wu, 2001). The microstrip line and planar form waveguide are linked together

through a tapered transition. A diagram of this transition is given in figure 2.9. Their

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results show a 12% bandwidth for a return loss less than 20dB centered around

28GHz with an insertion loss better than 0.3 dB.

Figure 2.9: Transition between microstrip line and dielectric-filled waveguide

(Deslandes and Wu, 2001).

Huang et al. have designed a transition between a microstrip line and a SIW

using a tapered transition in the Ku-Band (Huang et al., 2010). The transition they

designed is different than the one described above (Deslandes and Wu, 2001) A

sketch of transition is given in figure 2.10

Figure 2.10: Transition between a microstrip line and a SIW (Huang et al., 2010)

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Their results show a return loss of less than 15dB between the frequencies 1l-

14GHz for a back-to-back transition. Over the same frequency band the insertion loss

better than 0.7dB for the back-to-back transition.

Figure 2.11: Back-to-back transition between a microstrip line to SIW (Huang et al., 2010)

Deslandes & Wu have planned a transition that connects a grounded coplanar

waveguide to a SIW (Wu, 2005). The transition is composed of a current probe that

descends from the grounded coplanar waveguide to the bottom ground plane of the

SIW. The current flowing through the probe makes a magnetic field inside the SIW.

This magnetic field matches the TE mode magnetic field in a waveguide and

propagates through the SIW. A diagram of the transition between the two structures is

given in figure 2.11.